This addresses various real-world problems with HDF5 pkg-config, including
* hdf*.pc with package versions as part of the filename
* malformed hdf*.pc missing the commonly-used HDF5 HL module
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Additionally, this refactors more complicated dependencies such as
HDF5 and OpenMPI. This may help us deduplicate internal dependency
code in the future.
HDF5 selftest: improve platform-agnostic test
ci: init demo github action for HDF5 framework
ci Actions: hold off on MSYS2 for now [skip ci]
hdf5: ensure C libraries always included
ci: mac hdf5--use clang+gfortran